Blood and respiration (1978)

e [Music] there was a tantalizing glimpse of the past of the physiological society's 1976 centinary meeting when an early film was presented showing Professor later to be sir Joseph Barcroft demonstrating his method of determining the dissociation curve of the hemoglobin oxygen system this was an exp expent he carried out many times in the mountains of Peru and tenar when in the early part of this Century he was investigating the effect high altitude had on the blood work which was to lead to the publication of his well-known textbook the respiratory function of the blood the film which was found by chance in an obscure corner of Cambridge was made by Sir Joseph in his own Laboratories in the mid 1930s it has now been examined and compared with his published papers by Sir Joseph's son Professor Henry Barcroft and by Dr Peter goodford Dr Frank Norrington and others in the biophysics and biochemistry Department of the welcome Research Laboratories the commentary which has been added is an attempt to clarify the film for modern audiences and interpret the original scientific experiment as Faithfully as possible it is spoken by Professor Henry Barcroft when my father LED scientific Expedition to remote parts of the world he had to develop robust but lightweight equipment which he could take anywhere and which could produce a full oxygen dissociation curve from a small amount of blood the admiring onlooker on the right is Dr Adrien later to become Lord Adrien on the Rex this side he would normally Mount eight barro differential monometer although for this demonstration he is using only one the barro differential monometer was a forerunner of the warberg monometer since both sides were sealed it had the advantage of being automatically compensated for temperature variation and was unaffected by changes in barometric pressure it was therefore ideal for use in the field however because it worked neither at constant pressure nor constant volume the mathematics were somewhat complicated and perhaps this was the reason why it was not more widely adopted this tubular vessel is a tonometer which can be used to equilibrate a small blood sample with the gas mixture inside a finel serves as a convenient Mercury Reservoir although the health authorities might have something to say about it today [Music] for [Music] now he has a tonometer filled with nitrogen his test sample is probably blood which he will already have defibrinated by whipping with a feather or a wire brush alternatively it might be a solution of hemoglobin we can't be sure either way it makes little difference to the demonstration to make the gas mixture required he must introduce oxygen in the form of air into the the tonometer at the moment he is only measuring the volume of air approximately he will analyze it later [Music] [Music] now for his blood s [Music] [Music] [Music] notice how careful he is to preserve a drop of mercury in the bottom this will enable him to purge air from the tap when he comes to remove the sample for analysis now before continuing with the experiment proper my father is going to digress a little and show us the effect temperature has on the oxygen hemoglobin equilib blood in contact with air is fully oxygenated and bright red as the reference sample at the top shows the fact that they are both the color of arterial blood indicates that even with the small volume of air present in the testometer the solution is largely saturated with oxygen in the cold but now it is a different story at a higher temperature the reference sample is still bright red but the test sample has turned the dark red of Venus blood in other words heat is driven off the oxygen by all in the shape of the dissociation curve and this effect is reversible but now back to the main [Music] experiment for [Music] [Music] although you can't see it the little tube contains two Chambers into one of these he can introduce potassium feric cyanide in such a way that it only comes in contact with the blood after the monometer has been sealed the theide drives off all the bound oxygen causing a deflection on his monometer and the experiment was ingeniously designed to be independent of the quantity of blood present in the tube so now he can calculate the degree of saturation of the blood with oxygen he wants to plot this degree of saturation against the partial pressure of oxygen in the gas above and a conventional holdan gas analyzer forms part of his traveling apparatus see how he has inverted his tonometer so as to draw off the gas phase instead of of the liquid so now he can start to plot his dissociation curve the vertical axis is the percentage saturation of the hemoglobin in the sample with oxygen and this he plots against the oxygen partial pressure with eight monomers and eight tonometers each containing a different amount of oxygen he could and frequently did plot a full dissociation curve the curve which is the key to understanding the respiratory function of the blood this old film then gives us just a glimpse of how Joseph barro conducted his pioneering research both in his laboratory and in Expeditions which he led to many remote and inhospitable corners of the world [Music]